The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-191579 filed on Jun. 25, 2001 the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a four-stroke internal combustion engine having a valve resting mechanism for a valve lifter. More particularly, to a four-stroke internal combustion engine which includes a relative positional adjustment structure between an intake or exhaust poppet valve stem and a valve lifter, or in other words, a gap adjustment structure.
2. Description of Background Art
A valve motion apparatus with a top end of a stem of an intake or exhaust poppet valve pressed down by a valve motion cam with a valve lifter interposed therebetween to drive the intake or exhaust poppet valve to open or close and the intake or exhaust poppet valve is rendered inoperative when necessary is disclosed in Japanese Patent Laid-Open No. 184327/1998 and is advantageous in that it is compact and involves a number of parts.
In the valve motion apparatus, in order to adjust the relative positional relationship between the stem of the intake or exhaust poppet valve and the valve lifter, a shim for gap adjustment is interposed between a top end of the stem of the intake or exhaust poppet valve and a top wall of the valve lifter.
In an OHC (overhead cam) type four-stroke internal combustion engine provided with a valve lifter, where a valve resting mechanism is provided for the valve lifter, the height in the direction of an axial line of the valve increases. This is likely to cause deterioration in incorporating the valve lifter in a vehicle because of an increase in the head height particularly in a high compression ratio four-stroke internal combustion engine having a small valve included angle.
Further, a valve lifter provided with a valve resting mechanism has a weight increased by the weight of the valve resting mechanism when compared with another valve lifter which is not provided with a valve resting mechanism. In addition, the weight of the shim is added to this construction. Consequently, the equivalent weight of the intake or exhaust poppet valve and so forth increases and the valve spring load increases. As a result, an increase in the friction loss of the valve motion apparatus cannot be avoided.
Furthermore, since a shim is interposed between a valve lifter of a complicated structure which has a built-in valve resting mechanism and a top portion of an intake or exhaust poppet valve, a mounting operation of the shim is cumbersome and it is difficult to perform the mounting operation readily in a short time.
The subject to be solved by the present invention is to overcome the difficulties described above.
According to the present invention, a four-stroke internal combustion engine with a valve resting mechanism is provided wherein a valve lifter having a valve resting mechanism is interposed between a valve motion cam and a stem of a poppet valve. A valve lifter spring is provided for biasing the valve lifter in a direction in which the valve lifter is normally held in contact with the valve motion cam. A slide pin holder presses against the valve lifter by a spring force of the valve lifter spring that is provided on the valve lifter while a shim portion having a different thickness for controlling a relative positional relationship with the valve lifter is formed integrally with a top wall of the valve lifter. One of a plurality of different valve lifters which is most suitable for the relative positional relationship between the slide pin holder and the valve lifter is selectively mounted to effect a tappet gap adjust.
Since the present invention is configured in such a manner as described above, even if a shim is not prepared separately, a tappet gap adjustment is performed.
Accordingly, the height of the cylinder head is reduced by an amount corresponding to the thickness of a shim, and a reduction in the overall size of the internal combustion engine can be achieved.
Further, since no shim is used, the equivalent weight of each of the intake and exhaust poppet valve systems is reduced, and the valve spring load is reduced. As a result, the friction loss of the valve motion apparatus decreases.
Furthermore, since there is no necessity to provide a shim for the valve lifter, the man-hours for assembly are reduced and the productivity is augmented.
Further, the present invention is configured in such a manner wherein a valve resting mechanism operates with certainty and is simple in structure is obtained.
Furthermore, where the present invention is configured in such a manner wherein since no shim is provided for the poppet valve side with a valve resting mechanism wherein the distance from the poppet valve to the cam is liable to become long if a valve resting mechanism is provided. Thus, an increase in the height of the cylinder head can be suppressed thereby to achieve a reduction of the overall size of the internal combustion engine. Meanwhile, a shim is provided for the poppet valve side which normally performs an opening and closing motion and wherein there is no possibility that the distance from the poppet valve for which no valve resting mechanism is provided and which normally performs an opening and closing motion to the cam that may increase so that a single type of valve lifter can be used. Consequently, inventory control of valve lifters can be simplified.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.